The present invention relates generally to pneumatic tire tread made of styrene-rich styrene-butadiene copolymer rubber which may be blended with butyl rubber, butyl halide rubber or butadiene-acrylonitrile copolymer rubber or mixture thereof and which is added with petroleum-based processing oil and carbon black in high ratio for improving road gripping performance, and more particularly to such tread rubber composition further added with an ester so as to stabilize grip property despite of temperature fluctuation with keeping satisfactory mechanical strength of tire tread.
Hitherto various proposals have been made with respect to dynamic performances of the tire tread, above all grip property which is naturally related to accelerative and braking properties from the view points not only of tread patterns but also of tread rubber compositions.
As is well known to those skilled in the art, one of the important proposals is using of such rubber as higher glass transition temperature such as styrene-rich styrene-butadiene copolymer, and the others is the addition of petroleum-based processing oil and carbon black in higher ratio.
However, the former has been found unsatisfactory in that the grip property considerably declines as the temperature of the tread rubber is raised, or in other words the dynamic performance, such as grip property is not stable. The latter has an important disadvantage in that mechanical strength is considerably deteriorated when such fillers are added in such a higher ratio as being able to improve grip property.